How To: Run in a New Dirt Bike Engine

If you have just forked out the cash for a new bike or engine rebuild, you'll want to make sure you do things right by correctly running your dirt bike in.

The motors of motocross and enduro bikes are designed to be ridden hard and on the limit, however a fresh engine - whether it's off the showroom floor or recently been rebuilt - needs to be cared for in its early stages.

A 'run-in' or 'break in' period is necessary before you push the thing to its limits, and there are varying techniques around and everybody seems to have their own way of doing things. In this guide, we share a few key pieces of information to eliminate any uncertainty as to how to get your bike ready to rip!

Why should I run in my new dirt bike engine?

All of the moving parts in your engine and gearbox need a period of time to wear in, as the parts are made individually and then assembled in a factory.

In your gearbox, there may be some sharp edges from production which will wear down after some running time. The top end of the motor requires a few heat cycles as well to ensure all moving parts have had the chance to warm to operating temperature and then cool down as an assembled unit.

Forged and cast pistons:

There are two types of pistons which cover the majority of dirt bikes and they both require run-in periods, but for different reasons. The two types are forged and cast pistons.

Cast Pistons: Come standard in most two stroke engines, and the run-in time for cast is less about the piston and more about wearing the piston rings into the bore. A machined finished bore is slightly more abrasive than one with a few hours on it, and your piston rings need to go through a few heat cycles before they are properly hardened.

So if you skip the run-in period, you run the risk of excessive wear to your piston rings causing an improper ring seal resulting in blow-by, loss of power, and on a four-stroke, oil contamination.

Forged Pistons: When a forged piston is manufactured, hot metal is forced under extreme pressure into the shape of a piston. As this metal is not evenly heated during production, some parts of a freshly forged piston are less dense than others.

When the forged piston is first warmed up inside the engine, the different densities expand more or less causing the piston to expand unevenly. Warming the bike up slowly will help the piston wear into the shape of the bore once hot preventing the piston becoming out of round.

Therefore if you skip the run-in period, the worst-case scenario is that you can cause an engine seizure, which is the last thing you want!

How do I run-un my new motocross engine?

Here’s how we do it:

Step 1: Start the engine with the bike stationary and allow the engine to warm up to operating temperature (the top of the radiator hot to the touch).

Do not allow the engine to run at one RPM for an extended period of time, constantly vary the RPM and do not allow the engine to idle. For two strokes, revving the bike slightly higher briefly to clear the motor out is a good idea to avoid fouling a spark plug, but first allow the motor to warm up and avoid excessive revving.

When the engine reaches operating temperature (about 3-5 minutes of running time), turn the bike off and allow the motor to completely cool down, one hour at minimum is ideal.

Step 2: Start the engine with the bike stationary and allow the engine to warm up to operating temperature, once warm take your bike out for a ride.

Follow the same rule of constantly varying your RPM, run through the range of gears but do not rev the bike completely out. We suggest taking it to half throttle frequently and occasionally up to three-quarters of full throttle.

After 15 – 20 minutes, turn off your bike and allow it to cool down completely, one hour being ideal once again. While your bike is cooling, take this time to check over your bike, go over all of the nuts and bolts to check tensions.

Check your tyre pressures, chain and spokes and once the bike is completely cold, check the radiator coolant and oil levels.

Step 3: Start the engine with the bike stationary and allow the engine to warm up to operating temperature, once warm take your bike out for a ride.

Follow the same rule of constantly varying your RPM, run through the range of gears, but do not rev the bike completely out. We suggest taking it to three-quarters of full-throttle frequently and occasionally up to full throttle but not held at full throttle for more than a second.

After 15 – 20 minutes turn off your bike and allow it to cool down completely for around an hour. While your bike is cooling, take this time to check over your bike again and go over all of the nuts and bolts to check tensions.

You may also want to use a torque wrench and check the tension on your engine head and barrel fasteners while you are at it, the correct torque settings for your bike are in your owners’ manual.

Step 4: You are ready to take the bike for a normal ride! You may want to go easy on it a little longer but by now everything should be heat treated and worn in, so it will be safe to ride your bike as you normally would.

After this ride we suggest to perform an oil change and replace the oil filter if your bike has one, after this amount of running time all of the gears and moving parts in the gearbox would have completely bedded together and the oil in the gearbox will be full of tiny metal fibres from the bedding in process.

Another reason to change the oil so soon is most new engines are filled with 'run-in oil', which is often a different weight than standard oil to assist with the run-in procedure. This oil loses its lubricating capability quickly so it is important you change it after your bike has been run in.

NOTE: If you have purchased a new bike or have just had your motor rebuilt, consult your mechanic regarding that particular bike’s run in requirements before you kick it over. All bikes are different so it is best to check with the place you got it from.

If you have any further questions regarding running a bike in or what oil to use don’t hesitate to contact the friendly team at MXstore